Should I leave it Stock?
Is it a waste of money to put an intake, 4 barrel, and headers on a stock 273?
Yes and no.
It's not exactly a waste; it's just that;
the stock cam/carb/intake is good to say 3000rpm, so the 4bbl is not gonna do much until the 2bbl gives up..
and because of the small factory cam, headers are not a big help either. Taken together, you will get a power increase, but not until later in the rpm band.
I'm assuming you have an automatic, so with a stall of say,1700 rpm, neither of those is gonna make a difference at zero mph when you hammer the throttle.
I'm assuming you have 2.76 rear gears and with those 15s, you might be looking at final drive gearing of 65=2200. If that is true then 2500 in first gear, where the power is just starting, will be over 20 mph. So from zero to 20ish mph, that 4bbl and headers is not gonna help you one tiny bit.
That 273 cam might power peak at 4000ish rpm, and the 1-2 shift might be 4400 so your power band is gonna be from no lower than 2500, to perhaps as high as 4400. So if you want rapid-transit to happen, you need to be in that band. The 4bbl, might not be fullopen until closer to 3000, and if you open it too soon or too fast, you will likely just bog down. Lets say you somehow make it happen at 2800. So then your 4bbl power begins at ~2800, peaks around 4000, and is rapidly falling off at 4400tops.
In first gear this is beginning at~24mph, peaks at 34mph and is falling away at 41 mph,
The question is; does that help you?
In second gear, the power plateau might be at ~ 3600 to 4200. With 2.76s this is about 52 to 72 mph. Hey nice passing gear. But check out the hole from somewhere around 36 mph to 52 mph, where your engine is gonna be struggling.Even with the 4bbl, cuz she is off the cam.
But think about this;
How much power can you truley expect with the 4bbl and headers? and where is it gonna come in at?
I'll guess no more than 20hp at 4000rpm, more likely is 12 to 15
I'll guess zero hp at zero mph with a 1700 stall
I'll guess the power is linear from 2800 to 4000, so 1.67hp per 100rpm. It won't be linear tho, with less real power generated at 2800 than at 4000, but I just want you to see the point.
So;
if you are looking for more power to take off with from a dead-stop, then the 4bbl/header combo is a bust.
But if you want passing power from 52 to 72, it's hard to say no, to ~18hp
So
Is it a waste on a stock 273?
Yes and no.
IMO, you would do way better with;
a higher stall TC to get the engine to where the torque is,at zero mph,and
a bigger rear gear to hurry your engine up onto the cam sooner, and to keep it there longer, and,
no matter what;the engine is gonna want a free-flowing exhaust. Whether you chose headers or free flow HP logs is not gonna be a big deal, but you gotta provide a path for the faster reving engine to get rid of it's greater volume of exhaust per measurement of time.
I came to love the 2800TC behind my 318-4bbl/stock cam smogger engine, that I used to have in my 68Barracuda, for a winter engine. I ran it with just about every gear from 2.76s to 4.30s. I think the 3.91s were my favorite, but most of the time, she ran with 3.55s or 3.23s . I didn't have 3.73s and I think those would have been a good compromise.
One winter, she ran with a 2.74 low-gear A998 and 3.23s; That was a real nice first gear combo. Sometimes I revved it to the moon tho before grabbing second, cuz second was a lil further away than it had been with the A904. The 3.23s gave me an extra 5 mph cruising speed for the same rpm. All-in-all tho,I think I liked the A904/3.55s better, with the slower cruising speed.
Now; should it be that you have a 4-speed, I would have given a slightly different answer. Small engines really benefit from more and closer spaced gears. But the basics above still apply.
As for me; I would not spend the money on a 4bbl and headers, until after the increased Stall, and after the gears, and after the free-flowing exhaust. THEN, I would do the 4bbl together with a slightly bigger solid-lifter cam, and, I would feed that 4bbl, fresh cold air; you can't make extra power with hot rarefied air..
